1. Field of the Invention
The invention refers to an apparatus and method for increasing the polarization components as well as a light guide unit and liquid crystal display by use thereof.
2. Related Art
Formerly, when obtaining a polarized light wave that means a light wave having polarization in polarized components, either s wave or p wave of polarized components has been absorbed by illuminating a ray of nonpolarized light to a polarizing plate. Consequently, in principle, more than 50% of illuminated light is not made effective use of and about 58% of illuminated light is absorbed in measured values. In a conventional liquid crystal display (LCD), not only a polarizing device (polarizing plate) for obtaining a polarized light by using the absorption of light but also a printing dot diffusing sheet is as a rule used, which makes further 20% of light not usable.
FIG. 15 shows LCD module 100 of a conventional LCD device. Since light generated in the light source 101 exhibits approx. 96% of transmittance in the light guide plate 102, approx. 80% of transmittance in the diffusing sheet 103, approx. 42% of transmittance in the lower polarizing plate 104, approx. 40% of array opening ratio in the glass base plate 105, approx. 30% of transmittance in the color filter 106, and approx. 90% of transmittance in the upper polarizing plate 107, the actually usable luminous intensity becomes 3.5% of the light generated in the light source 101, which smallness constitutes a large hindrance to an effective use of energy. Especially, in a portable personal computer, it is an important theme to secure a longer serviceable time for a fixed battery charging amount. Since a consumed power of the backlight 108 has a large proportion in the whole consumed power, a backlight system to be used in a high-brightness and low-power-consumption liquid crystal display (LCD) is eagerly desired.
A light energy absorbed in the lower polarizing plate 104 and the like comes to be converted into thermal energy and this generated heat becomes a factor for deteriorating parts of the LCD device. In particular, liquid crystals of STN (Super Twisted Nematic) type has a property of deterioration in indication quality due to heat and therefore it is also an important theme to reduce such generation of heat.
In this conversion of luminous energy into thermal energy, 66.4% of the luminous energy (69% of heat generation due to luminous energy) arises from the absorption of light in the lower polarizing plate 104 and diffusing sheet 103 as shown in FIG. 15.
Japanese Published Unexamined Patent Application No. 4-271324 shows one technique for enhancing an effective use of light, in which a light guide comprises a plurality of laminated refracting layers having different refractive indices and a decrease in optical packet is reduced by allowing a ray of light incident from a light incident end surface to be refracted on the boundary surface of each refractive layer and to reach the outgoing surface at a smaller angle than the critical angle, thereby promoting the light utilizing efficiency.
Also in Japanese Published Unexamined Patent Application No. 2-201316, the light utilizing efficiency of a light source is promoted by reducing the transmission of polarizing plate to once as a result of comprising a liquid crystal cell, a light guide plate disposed therebehind, a colored filter provided on the light guide plate, a reflecting-plate attached polarizing plate provided on the rear face side of the light guide plate, and a light source provided on the lateral face of the light guide plate.
However, either of these techniques is not different from the prior art described before in that no light comprising many polarized components is illuminated on the polarizing plate and a polarized light is obtained by absorbing either s wave or p wave, and does not enable at least a part of this absorbed and not-to-be-used component to be used.
Incidentally, some conventional backlight systems containing the order of 2.7% of polarized components are seen but these have no intention to polarize the light from a light source in the backlight.
As techniques for obtaining a polarized component by using characteristics of reflection or transmission without polarizing plate, there are a polarized beam splitter (PBS), transmission-type linear polarizer, and the like. Even though able to make use of only either s wave or p wave of light, or to make use of each separately, neither of these technique can make an effective use of both together.
Meanwhile, in a conventional transmission-type linear polarizer, because incident light is made to directly enter the polarizer at a Brewster's angle, it is impossible to diffuse a converged light onto a wide outgoing surface for outgoing. Furthermore, because a troublesome treatment is required for making the system thinner, no technique for obtaining a polarized light without using such a polarizing plate has so far been utilized for a light guide unit of the LCD device.